Sweetening process using nitrogen oxide catalyst



to handle and store.

United States Patent 3,244,618 SWEETENING PROCESS USING NITROGEN OXIDE CATALYST Harold L. Dimond, Pittsburgh, Herbert B. Fernald,

Glenshaw, and Raynor T. Sebulsky, Verona, Pa., assiguors to Gulf Research 8: Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Filed Apr. 22, 1964, Ser. No. 361,879 9 Claims. (Cl. 208207) This invention relates to a process for reducing the mercaptan content of hydrocarbons and is particularly applicable to the treatment of hydrocarbons of petroleum origin. The process can therefore be applied to lower ing the mercaptan content of such diverse stocks as liquefied petroleum gases (LPG), sour gasolines (such as cracked gasoline, sour natural gasoline, straight run gasoline or mixtures threof), naphthas, solvents, jet fuels, kerosenes, and furnace oils.

Petroleum-derived hydrocarbons frequently contain elemental sulfur and sulfur compounds, such as hydrogen sulifide, mercaptans, organic sulfides and disulfides. In general, sulfur compounds are undesirable in petroleum hydrocarbons. By petroleum hydrocarbons herein we intend to include distillates such as gasolines, naphthas, kerosenes, jet fuels, and furnace oils which are derived from petroleum, as well as LPG and natural gasolines which may have as their source natural gas wells. Among the sulfur compounds present in petroleum hydrocarbons, hydrogen sulfide and mercaptans are espectially objectionable. This is because they impart unpleasant odors to petroleum hydrocarbons even when present in very low concentrations. Furthermore, the presence of hydrogen sulfide and mercaptans Will frequently result in petroleum hydrocarbons being corrosive and, thus, difiicult Hydrogen sulfide can readily be removed by caustic washing. Some lower boiling mercaptans can also be extracted fairly readily by caustic washing. Higher boiling mercaptans, however, can not be readily extracted by caustic washing. This is because mercaptans are weak acids whose acidities decrease rapidly as their molecular weights increase. Frequently, mercaptans can be removed satisfactorily from very light petroleum hydrocarbons, like LPG, by caustic washing, because only very light mercaptans are present. For somewhat higher boiling hydracorbons, such as light gasolines, only limited removal of mercaptans is generally obtained by caustic washing, even in the presence of solutizers. mercaptans, they are frequently converted to disulfides, which are relatively odorless, by a sweetening process. By definition, a petroleum stock is sweet if it passes the doctor test. This test is sensitive to the presence of mercaptan sulfur or hydrogen sulfide in concentrations of five to 10 parts per million.

The doctor test can be described briefly as follows. A sample is shaken with a sodium plumbite solution in a test tube. If hydrogen sulfide is present, PbS will precipitate as a black solid. If PbS does not precipitate, the presence of mercaptan can be detected by adding a pinch of flowers of sulfur and shaking. If mercaptans are present, PbS will precipitate. The test solution and recommended procedures are described more fully in UOP Labortatory Test Methods for Petroleum and Its Products, 4th edition, 1959, edited by D. P. Johnson, Jr., and

Because of the difiiculty of removing r published by the Universal Oil Products Company, Des Plaines, Illinois.

It is customary to require in the specifications of many petroleum products that they be sweet to the doctor test. In some cases, however, it is sufiicient and satisfactory to render a petroleum product odor sweet. This can be accomplished by reducing the content of hydrogen sulfide and mercaptan sulfur to a level of 20 to 50 parts per million. Thus, while it is relatively easy, by means of the process described herein, to sweeten a petroleum hydrocarbon so that it passes the doctor test, it is also possible to interrupt the sweetening reaction at any intermediate stage. The product will not be doctor sweet in such case, but the mercaptan content will be substantially reduced.

The invention defined herein relates to a procedure for sweetening petroleum hydrocarbons. The procedure involves treating a petroleum hydrocarbon with molecular oxygen in the presence of a catalytic amount of one or more nitrogen oxides selected from the group consisting of NO, N0 N 0 N 0 and N 0 As a result of such treatment, mercaptans are converted to disulfides. It is understood that this procedure can be used alone, in which case mercaptans initially present in the petroleum hydrocarbon are substantially converted to disulfides. Alternatively, this procedure can be used in conjunction with a caustic wash. In this latter case, only those mercaptans which are not extractable by the caustic are converted to disulfides, and a net reduction of the sulfur content of the petroleum hydrocarbon is effected.

As noted, the invention defined herein relates to a procedure for rendering the petroleum hydrocarbons sweet to the doctor test. Thus gasolines having the following specification'and including from about 0.0005 to about 0.5 percent by weight thereof of mercaptan sulfur can be treated in accordance with the process of this invention.

Gravity, API 27.0 to 100.0

Specific gravity, 60/60 F. 0.61 to 0.89 Vapor pressure, Reid, p.s.i.a. 5to 15 Distillation, gasoline:

Over point, F. to End point, F 340 to 430 Kerosenes having the following specifications and including. from about 0.0005 to about 0.50 percent by weight of mercaptans can be treated in accordance with the process of this invention.

Gravity, API 30.0 to 50.0 Specific gravity, 60/60 F. 0.779 to 0.876 Distillation, kerosene:

Over point, F. End point, F.

250 to 500 450 to 750 The amount of molecular oxygen that must be employed in the process of this invention is at least the amount stoichiometrically required to react with the rnercaptans to convert the latter to disulfides. Since, theoretically, four mols of mercaptans will react with one mol of molecular oxygen to form two mols of disulfide and two mols of water, it can be seen that at least about one-fourth 'mol of molecular oxygen must be ernplayed for each mol of mercaptan present in the light petroleum distillate to be treated. Stated another way, basing the amount of molecular oxygen required upon the amount of petroleum hydrocarbon to be treated, the amount of molecular oxygen stoichiometrically required is about 0.000125 to about 0.125 percent by weight. In the ordinary operation of this invention, molecular oxygen would normally be supplied in large excess. It would be seldom advantageous, however, to employ more than about two to about five weight percent of molecular oxygen, based on the particular petroleum hydrocarbon to be treated. The amount of introgen oxide required, based on the petroleum hydrocarbon to be treated is at least 0.000005 percent by weight, preferably about 0.000025 to about 0.25 percent by weight.

Temperature and pressure requirements for the procedure are not critical and the procedure is therefore preferably carried out advantageously at about room temperature and atmospheric pressure. While an elevated temperature may advantageously increase the desired reaction rate between the mercaptan and molecular oxygen, this is somewhat offset by the fact that at the same time molecular oxygen will have a tendency to escape from the reaction zone. In general a temperature of about 30 F. to about 150 F., preferably about 50 F. to about 90 F., can be employed. Pressure does not appreciably aflect the reaction rate, except that increased pressures facilitate movement of molecular oxygen into the petroleum hydrocarbon. In general a pressure of about to about 1000 pounds per square inch gauge, preferably about 0 to about 50 pounds per square inch gauge, can be employed. Reduced pressures can also be employed but offer no particular advantage.

Reaction time depends on both the quantity of mercaptan present in the petroleum hydrocarbon to be treated and upon the concentration of the nitrogen oxide catalyst used. With very low catalyst concentrations, the time required to convert substantial quantities of mercaptans to disulfides may be several days. At high catalyst concentrations less than 30 minutes may be required. In general, a catalyst concentration would be selected which produces a sweet product in 30 minutes to four hours. Thus, for our purposes we can employ a reaction time of about five minutes to .10 days, preferably about minutes to one day, but most preferably about 30 minutes to four hours.

The reaction is terminated easily by stopping the flow of molecular oxygen into the petroleum hydrocarbon and permitting the latter to stand without further agitation, or the reaction can be allowed to proceed to completion, in which case the reaction will be terminated by the disappearance of mercaptans. In order to remove excess dissolved nitrogen oxide from the petroleum hydrocarbon upon termination of the reaction, the same can be passed over a caustic material, such as lime, sodium hydroxide, etc. Alternatively, excess nitrogen oxide can be removed by passage of the treated petroleum hydrocarbon over such absorbing materials as activated carbon, clays, silica gel, alumina, etc.

The process can futher be illustrated by the following:

Example I Into a three liter flask equipped with a magnetic stirrer there was placed 600 cc. (412.2 grams) of natural gasoline having the following specifications:

Gravity, API 59.6 Specific gravity, 60/60 F. 0.7405

Reid vapor pressure, D323, p.s.i.a. 8.1. Hydrocarbon analysis:

Vol. percent aromatics 4.0 V 01. percent olefins 0.5 Vol. percent saturates 95.5 Distillation, D86:

Over point, F 108 50% point, F. 142 95% point, F. 216 End point, F. 249

Water content, wt. percent 0.0252

Over a period of five minutes there were added together 0.075 gram of N0 and 0.20 gram of oxygen. It was noted that the N0 was largely dissolved in the gasoline. Agitation with the magnetic stirrer was started, and the reaction was permitted to proceed at a temperature of F. and a pressure of five pounds per square inch. gauge for one-half hour. At the end of this time, the product was tested by the doctor test.

Example II Example I was repeated with 407.0 grams of the same gasoline and using 0.030 gram of N0 over a period of two hours. Evary half hour a sample was tested by the doctor test.

Example III Example III is also similar to the above, except that 410.7 grams of the same gasoline was employed and the amount of N0 used was reduced to 0.020 gram. For the first four hours, a sample was Withdrawn each half. hour and given the doctor test. After an additional 16 hours a sample was withdrawn and given another doctor test. Finally, the reaction system was permitted to stand for 10 days.

Example IV In Examples I, II and III the sweetening procedure.

of this invention was carried out in a glass flask under normal room illumination. To determine if light played an important role in initiating the reaction, a test was made duplicating Example II but exercising care to shield the flask from all illumination. Thus, during the reaction period the flask was completely enclosed in aluminum foil. The gasoline was not sweet in two hours but was doctor sweet in two and one-half hours. Thus, sweetening was only slightly slower in the absence of light, and it may be concluded that while light may somewhat accelerate the reaction it is not necessary for operation of the process.

Example V To demonstrate the applicability of the process to another petroleum hydrocarbon product 600 cc. (478.7 grams) of an Ordovician kerosene having the following specifications:

Gravity, API 47.1 Specific gravity, 60/60 F. 0.7923 Hydrocarbon analysis, D1319:

Vol. percent aromatics 10.5

Vol. percent olefins 1.0

Vol. percent saturates 88.5 Distillation, D86:

Over point, F 362 50% point, F 436 point, F 504 End point, F 521 H O content, wt. percent 0.0145

was treated in the manner of Examples I, II and III with' 0.040 gram of N0 and 0.20 gram of molecular oxygen. A doctor sweet product was obtained in one-half hour.

The results obtained from Examples I, II and III are set forth below in Table I, while the results obtained from Example V are set forth below in Table II.

TABLE I Product from Product from Product from Product from Charge, per- Example I, Example II, Example III, Example IV, cent by weight percent by percent by percent by percent by weight weight weight weight weight 0. 088 0. 083 0. 079 0. 082 0. 083 0.045 0.5 0.5 0.5 05 0. 007 0. 05 0. 052 0. 05 0. 055 0. 0005 0. 0005 0. 0005 0. 0005 0. 0005 0. 001 0. 001 N 02 employed, percent by Weight 0. 0186 0. 0074 0. 0049 0. 0074 O2 consumed, percent by weig 0.01 25 0.01125 0.01125 0.01125 Doctor test Sour Sweet Sweet Sweet Sweet Approximate time for sweetening, hrs 2 2 2% P.p.m. Days.

TABLE II tages over sweetening processes frequently employed in industry. Because the nitrogen oxide catalyst employed Product from in this process is very soluble in petroleum hydrocarbons, g ig fi ggg fg' it is only necessary to effect intimate contact between weight two phases comprising the petroleum hydrocarbon (which contains the catalyst in solution) and a source Total sulfur--. 0. ego 0.25; of molecular oxygen such as air. In many other procgggg figgjfig 8:85;, (1521 esses, i.e., copper chloride sweetening, air-inhibitor sweet- Elemental sulfur 0-0005 8-8ggi ening, air-solutizer sweetening, it is necessary to bring 33ti5s23.02153:1: 0.00665 n intimate Contact three P the third P being Doctor test. ur swelet elther a solid catalyst or a liquid such as caustlc solu- Appmxlmatetmem sweetemnghr A tion which is not miscible in the hydrocarbon phase.

1 P.p.m.

The doctor test was employed to determine that the treated petroleum hydrocarbon product was sweet. Note that the procedure defined herein was extremely effective for the conversion of the mercaptans to disulfides. The total sulfur content of the petroleum hydrocarbons was not materially disturbed by the treatment, nor were, as far as can be determined, the remaining sulfur com pounds present. It is also apparent that the N0 employed was in fact a catalyst and not a reactant, for the amount of oxygen present chemically combined with nitrogen present in the N0 employed in Examples II, III and IV would not be suiiicient to convert the mercap tans to disulfides even if it were postulated that the N0 completely decomposed to produce atomic or molecular oxygen. Although the remaining sulfur compounds are not identified, it is seen that their presence is not detrimental in the present context, for the treated petroleum hydrocarbon passed the doctor test.

The procedure defined herein is also unique in one particular aspect. As pointed out above, the conversion of mercaptan to disulfide is accompanied herein by the formation of water. In addition, both the gasoline and kerosene contained small amounts of water even before sweetening. While the amount of water is small compared to the amount of petroleum hydrocarbon that is being treated, the amount of water formed is relatively large in comparison to the amount of disulfides formed. It might have been expected, therefore, that with water present sulfonic acids would also have been formed. Sulfonic acids are extremely undesirable in petroleum hydrocarbon products because of their highly corrosive nature. However, we found no evidence that sulfonic acids were present.

We have disclosed the use of N0 in the procedure defined above. It must be pointed out that an equilibrium between N0 and N 0 exists over a relatively large temperature range (approximately 11 C. to plus 140 C.) at atmospheric pressure. At low temperatures, N0 becomes N 0 a honey-colored liquid. At higher temperatures, N 0 becomes N0 8. red-brown gas. Accordingly, whenever N0 is mentioned herein, N 0 is also intended to be covered thereby under conditions conducive to its formation.

The process described herein has a number of advan- Also, the present process is operable at low temperatures, typically at 70 to F., while some other processes require elevated temperatures. For example, doctor sweetening is usually done at F., and various hydrodesulfurization schemes require temperatures as high as 400 to 600 F. Finally, the catalyst employed is relatively inexpensive and is required in only very small concentrations. Thus, while recovery and reuse of the catalyst is possible in this process, it is not economically necessary.

Obviously, many modifications and variations of the invention, as hereinabove set forth, can be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for reducing the mercaptan content of a petroleum hydrocarbon which consists essentially in contacting said hydrocarbon with a gas comprising molecular oxygen and an effective catalytic amount of a nitrogen oxide selected from the group consisting of NO, N02, N203, N204 and N205.

2. A process for reducing the mercaptan content of gasoline which consists essentially in contacting said hydrocarbon with a gas comprising molecular oxygen and an efiective catalytic amount of a nitrogen oxide selected from the group consisting of NO, N0 N 0 N 0 and N 0 3. A process for reducing the mercaptan content of kerosene which consists essentially in contacting said hydrocarbon with a gas comprising molecular oxygen and an effective catalytic amount of a nitrogen oxide selected from the group consisting of NO, N0 N 0 N 0 and N205.

4. A process for reducing the mercaptan content of a petroleum hydrocarbon which consists essentially in contacting said hydrocarbon with a gas comprising molecular oxygen and an effective catalytic amount of N0 5. A process for reducing the mercaptan content of gasoline which consists essentially in contacting said hydrocarbon with a gas comprising molecular oxygen and an effective catalytic amount of N0 6. A process for reducing the mercaptanv content of kerosene which consists essentially in contacting said hydrocarbon with a gas comprising molecular oxygen and an effective catalytic amount of N0 7. A process for reducing the mercaptan content of a petroleum hydrocarbon which consists essentially in contacting said hydrocarbon with a gas comprising molecular oxygen and at least about 50 parts per'million Of 2.

8. A process for reducing the mercaptan content of gasoline which consists essentially in contacting said hydrocarbon with a gas comprising molecular oxygen and at least about 50 parts per million of N0 9. A process for reducing the rnercaptan content of kerosene which consists essentially in contacting said ,and at least about 50 parts per million of N0 References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Mallette, F. 8., Air Pollution, Reinhold, New York, 1955, pages 86 and 89-90.

Stern, A. C., Air Pollution, Academic Press, New York, 1962, vol. I, page 37; vol. II, page 145.

DELBERT E. GANTZ, Primary Examiner.

R. H. SHUBERT, Assistant Examiner. 

1. A PROCESS FOR REDUCING THE MERCAPTAN CONTENT OF A PETROLEUM HYDROCARBON WHICH CONSISTS ESSENTIALLY IN CONTACTING SAID HYDROCARBON WITH A GAS COMPRISING MOLECULAR OXYGEN AND AN EFFECTIVE CATALYTIC AMOUNT OF A NITROGEN OXIDE SELECTED FROM THE GROUP CONSISTING OF NO, NO2, N2O3, N2O4 AND N2O5. 